In this talk we will present an overview of recent development of ultrafast lasers sources and their applications. This talk
will highlight some recent state of the art ultrafast pulse results from Ti:Sapphire and Ytterbium based laser systems.
There are significant advantages in being able to directly diode pump Ytterbium materials resulting in more compact
bulk solid state and fiber based laser systems. Several newly emerging technologies such as Optical Parametric Chirped
Pulse Amplification, and Supercontinuum Generation have generated great excitement in recent years. The evolution of
more compact and user friendly ultrafast laser systems has enabled completely new fields that take advantage of the
extremely high peak powers and very short time duration of ultrafast laser pulses. Recent results in the fields of
multiphoton microscopy, micromachining, 3-D fabrication, and spectroscopy will be discussed.
Thermal effects are unavoidable in laser material processing and are present, to some extent, even in the case when ultra-short (sub-picosecond) pulsed irradiation is used. We discuss here the matters of high-precision energy delivery into micrometer-sized volumes for three-dimensional (3D) laser microfabrication. Precise account of the
absorbed energy, pulse duration, and focal spot size allows to optimize laser processing parameters. As an example, a 3D micro-structuring of silica with better than 15 μm resolution is demonstrated by pulses of 11 ns duration and 266 nm wavelength (for a focusing by a low numerical aperture NA = 0.029 lens). The two photon
absorption coefficient of silica, β ≃ 60 ± 10 cm/GW, at 266 nm has been determined. The thermal black-body type emission of non-equilibrated electrons is discussed as a possible light source for 3D modification and structuring of photo-sensitive and photo-polymerizable materials. It is also demonstrated that optical properties of ionized dielectrics can be used to determine the temperature.
Carbon nanocomposites consist of thermoset and thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, an Yb:KGW solid-state femtosecond laser and an Nd:YVO<sub>4</sub> solid-state nanosecond laser were used to micromachine oxidized multi-wall carbon nanotube (MWCNT) doped morthane. The experimentation studied the relationship between various laser-processing parameters including laser pulse duration, pulse energy, beam scanning speed, and average power. The processing consisted of cutting channels into the materials using 1048 nm wavelength at 400 fs pulse duration, 1064 nm wavelength at 40 ns pulse duration, and 355 nm wavelength at 35 ns pulse duration. Additionally, the effects of oxidized MWCNT fill percentage were considered. The material removal rate was quantified for each experimental condition. The experimental results are discussed in terms of material removal rates, machining quality, and achievable feature size.
Carbon nanocomposites consist of thermoset and thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This new and innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, Nd:YAG and Nd:YVO<sub>4</sub> solid-state lasers were used to micromachine carbon nanocomposite thermoplastic materials. Experimentation was completed to compare the ability to laser micromachine carbon nanomaterial, carbon black, and unfilled polyurethane. The experimentation studied the relationship between repetition rate, travel speed, and material removal rate. The processing consisted of cutting channels into the materials using an Nd:YVO<sub>4</sub> laser at 1064, 532, and 355 nm wavelengths. The material removal rate and groove width were quantified for all wavelengths and compared versus the experimental variables. Trials were also completed on laser machining deep channels using an Nd:YAG laser and polyetheretherketone (PEEK) filled with carbon black and carbon nanofiber. The results of the experimentation show similar material removal rates for carbon black and carbon nanofiber filled polyurethane. The PEEK material exhibited high aspect ratio channels with both carbon black and carbon nanofiber fillers. Laser micromachining of polymers whcih were previously unmachinable using infra-red has been demonstrated.
This paper presents the results of recent efforts to improve the biocompatibility and integration of implantable bioMEMS devices. Laser micro-grooves and micro-grids were irradiated onto silicon surfaces using ultraviolet lasers. The micro-textured surfaces were then coated with nano-scale layers of titanium to promote improved biocompatibility. The micro-groove geometries have been shown to promote contact guidance, which leads to reduced scar tissue formation. In contrast, smooth surfaces result in random cell orientations and the increased possibility of scar tissue formation. The nature of the cellular attachment and adhesion to the coated/uncoated micro-textured surfaces was elucidated by the visualization of the cells through scanning electron microscopy. Finally, the implications of the results are discussed for integration of silicon-based microelectronics and sensors into biological systems.
Carbon nanocomposites consist of thermoset or thermoplastic materials filled with carbon nano-particles (nanotubes, bucky balls, etc.). This new and innovative group of materials offers many advantages over standard polymers such as electrical/thermal conductivity and improved structural properties. In the current study, direct diode and Nd:YAG solid-state lasers were used to transmission weld -carbon nanocomposite materials. The experimentation was focused on exploiting the infrared absorbing characteristics of the carbon nanocomposites. Polyetheretherketone (PEEK) based polymer was used in the initial experimentation to quantify weld strength. The experimentation included a complete analysis of the transmission characteristics of the base polymer at 810 nm and 1,064 nm wavelengths, an optical microscope view of the weld cross-section, and transmission welding experimentation. The transmission welding experimentation studied the relationship between average power, travel speed, and weld peel strength. A micro-channel welding experiment was also completed using a polycarbonate (PC) based polymer. The experimentation qualified the minimum feature size that could be joined. The resulsts show that the carbon nanocomposites can be welded in a similar way to carbon black filled materials. The carbon nanocomposites exhibited higher peel strengths at lower average laser power at both 810 and 1064 nm. The carbon nanocomposite material exhibited a unique characteristic of being able to be machined and welded by the same laser wavelength.
Laser micromachining of semiconductor materials such as silicon and sapphire has attracted more and more attention in recent years. High precision laser cutting and drilling processes have been successfully used in semiconductor, photonics, optoelectronics, and microelectromechanical system (MEMS) industries for applications including wafer dicing, scribing, direct via forming, and three-dimensional structuring. In the current study, Q-switched diode-pumped solid-state (DPSS) lasers have been used to scribe grooves on silicon wafer substrates at different pulsewidths (10 and 32 ns), pulse repetition rates (30, 40, and 50 kHz), focal lengths (100 and 53 mm), and wavelengths (355 and 266 nm). Experimental results have been compared between different laser parameters including pulsewidth, power level, pulse repetition rate, and wavelength. It has been found that at the same average power and same repetition rate, the grooves scribed by the longer pulsewidth laser are deeper, while the shorter pulsewidth laser produces better quality cuts. However, the same short pulsewidth laser can produce deeper grooves by increasing its repetition rate and power. Moreover, given the same laser parameters, the shorter focal length objective produces deeper grooves than the longer focal length one but it does not reduce the feature size proportionally due to the complications induced by debris and recast materials. Finally, with the same optical set-up and laser output parameters, it appears that the 266 nm laser does not provide obvious advantage when compared to the 355 nm laser in these particular silicon scribing experiments. The implications of these results are also discussed.
Liquid crystal polymer (LCP) is a new and innovative material being used as an alternative to polyimide in the flexible circuit industry. LCP has many intrinsic benefits over polyimide including lower moisture absorption and improved dimensional stability. However, LCP is very resistant to chemical milling or etching. As a result, other methods for processing the material are being investigated including laser micromachining. In this paper, three frequency converted diode-pumped solid-state (DPSS) Nd:YVO<sub>4</sub> lasers at 355 nm were used to micromachine a LCP film and a copper/LCP laminate. Of them, two are Q-switched lasers operating in the nanosecond regime and the other a mode-locked laser in the picosecond regime. The Q-switched lasers can be operated at pulse repetition rates of 1 to 300 kHz while the mode-locked system is operated at 80 MHz. The micromachining experiments consisted of cutting the 50 μm thick LCP film, cutting the 18 μm thick copper on the film, and drilling micro-vias through both the copper coating and the film substrate. The laser/material interactions and processing speeds were studied and compared. The results show that, compared to polyimide film of the same thickness, LCP film can be more efficiently processed by laser micromachining. In addition, each laser has a unique advantage in processing LCP based flexible circuit materials. The Q-switched lasers are more capable of processing the copper coating while the mode-locked laser can cut LCP film faster with the smallest kerf width.
During the last decade, diode-pumped TEM<sub>00</sub> mode solid state lasers have gained widespread application in micromachining of dielectrics and metals. Commercial systems with output powers of up to 40W at 1064nm, 20W at 532nm, 15W at 355nm and 2W at 266nm, repetition rates of up to 400kHz and pulse durations between 10ns and 100ns are now being used in numerous micromachining applications. In addition, industrial applications of modelocked lasers are starting to emerge. This paper will give an overview of the state-of the art of diode-pumped TEM<sub>00</sub> mode solid state lasers and their applications in micromachining.
The current paper presents the results of recent studies of the effects of laser processing parameters on the microstructure and surface topology of laser grooved Ti-6Al-4V surfaces used for biomedical applications. Laser micro-grooves are produced using a diode pumped solid state (DPSS) lasers at 355 nm and different pulse repetition frequencies (PRF). The underlying microstructures and surface topologies of the grooves are then characterized using scanning electron microscopy (SEM). Laser/material interaction mechanisms are discussed and optimal laser processing parameters are developed. The implications of the microstructural and topological features are then assessed for cell/surface interactions and adhesion.